This invention relates to semiconductor light emitting devices and methods of fabricating semiconductor light emitting devices, and more particularly to packages and packaging methods for semiconductor light emitting devices.
Light emitting diodes and laser diodes are well known solid state electronic devices capable of generating light upon application of a sufficient voltage. Light emitting diodes and laser diodes may be generally referred to as light emitting devices (“LEDs”). Light emitting devices generally include a p-n junction formed in an epitaxial layer grown on a substrate such as sapphire, silicon, silicon carbide, gallium nitride, aluminum indium gallium nitride, gallium arsenide, aluminum indium gallium arsenide, aluminum indium gallium phosphide, and the like. The wavelength distribution of the light generated by the LED generally depends on the material from which the p-n junction is fabricated and the structure of the thin epitaxial layers that make up the active region of the device.
Typically, an LED chip includes a substrate, an n-type epitaxial region formed on the substrate and a p-type epitaxial region formed on the n-type epitaxial region (or vice-versa). In order to facilitate the application of a voltage to the device, an anode ohmic contact is formed on a p-type region of the device (typically, an exposed p-type epitaxial layer) and a cathode ohmic contact is formed on an n-type region of the device (such as the substrate or an exposed n-type epitaxial layer).
An LED chip emits optical energy having a relatively narrow bandwidth. Accordingly, light emitted by an LED chip is highly saturated light that appears to have a single color. However, it is desirable in many applications to generate white light using solid state light emitting devices, such as LEDs. White light is a combination of different wavelengths of light.
Light that appears white to an observer can be generated by surrounding a blue LED chip with a wavelength conversion material such as a phosphor. At least some of the light emitted by the LED at a first wavelength (primary light) may be absorbed by the phosphor, which may responsively emit light at a second wavelength (secondary light). The primary light emitted by the LED chip and the secondary light emitted by the phosphor particles may combine to produce light having a plurality of wavelengths, and that may be perceived by an observer as having a different color than either the primary light or the secondary light. For example, if the primary light is blue and the phosphor is selected to generate a yellow light in response to stimulation by the blue primary light, the resulting combination of light emitted by the package may appear white, or nearly white, to an observer. However white light that is generated in such a manner may not be capable of illuminating objects well.